1. Field of the Invention
The present invention relates to a mobile communication system, and more particularly, to a method of estimating a Doppler frequency shift and a method of transmitting data using the same.
2. Background of the Related Art
Typically, if a moving transmitting end transmits a radio wave to a receiving end, the frequency of the radio wave received by the receiving end has a different range from that of the frequency when the radio wave is transmitted. This is called a Doppler frequency shift phenomenon.
At this time, two essential elements that determine the degree of the Doppler frequency shift are a frequency that the transmitting end uses, and a moving speed of a moving receiving end. The used frequency and moving speed are in direct proportion to the Doppler frequency shift. That is, as the used frequency becomes higher and the moving speed becomes higher, the Doppler frequency shift appears greater.
However, since the used frequency is not changed in the general mobile communication system, the degree of the Doppler frequency shift is changed simply in accordance with the moving speed of the receiving end.
The Doppler frequency shift may be construed as the occurrence of the difference between the frequency range used to transmit a signal and frequency range in receiving the signal, and thus a great Doppler frequency shift means that there is a great difference between the transmission frequency and the receiving frequency. Also, the great Doppler frequency shift means that the moving speed of a terminal to receive the signal is higher than as usual on condition that the transmission frequency is unchanged.
In other words, the higher moving-speed of the terminal indirectly indicates that the channel communication environment is not good, e.g., a communication condition of a channel is rapidly changed.
The channel communication environment rapidly changed is directed to an unstable state, and this unstable state means that it is difficult to satisfy a desired quality level of the received data. This is because it is difficult to compensate for and obtain the quality of the desired level through the conventional power control technique with respect to a change of the channel communication environment having a greater level than a specified level.
However, the conventional communication system does not adopt a transmission method based on a Doppler frequency shift value according to a moving speed of a terminal to receive a transmission signal.